Many modern speech recognition systems use a restrictive language specification, such as a context free grammar (CFG). These grammars are powerful enough to describe most of the structure in spoken language, but also restrictive enough to allow efficient recognition and to constrain the search space.
Such grammars are an integral part of the speech system in that they are closely tied to the underlying technology in the speech system. Therefore, the grammars are a critical factor in determining the quality of service that is delivered by the speech system.
The worldwide web consortium (W3C) has defined an industry standard XML format for speech grammars. Some examples include: